Re: No Listener in constructor

Daniel Pitts <>
Tue, 23 Oct 2007 09:51:35 -0700
Philipp wrote:

I heard that one should not register an object as a listener for some
events during its construction because an event could be triggered
before the object is completely constructed.

What do you think about this?

Thanks Philipp

For one thing, it is a thread safety issue. Along with the general
practice that you should not allow the "this" pointer to escape during
construction. The "this" pointer is only fully valid once the
constructor has completed normally. If you need to register listeners
as part of the instantiation process, consider using a static factory
method which instantiates a private constructor, and then attaches that
instance to the appropriate places.

If you want an indepth explanation of why it is dangerous, along with a
lot of other good-to-have understanding of multi-threaded programming, I
suggest getting the book /Java Concurrency In Practice/. You can read my
short review of it at

Good luck,
Daniel Pitts' Tech Blog: <>

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